Multi-board optical transceiver

ABSTRACT

A transceiver module including a primary printed circuit board and a secondary printed circuit board in an enclosure is presented. The primary printed circuit board is coupled to the secondary printed circuit board by a connector pin that protrudes out of a critical surface of the enclosure. The printed circuit boards may be positioned substantially parallel to the critical surface of the enclosure. When a transmitter is electrically connected to the primary printed circuit board and a receiver is electrically connected to the secondary printed circuit board, the transmitter and the receiver may be positioned in a plane that is also substantially parallel to the plane of the critical surface.

BACKGROUND

[0001] The invention relates generally to optoelectronic/opticaltransceivers and particularly to optoelectronic/optical transceivermodules that benefit from an efficient use of module space.

[0002] Today, communication systems using optical fiber as a means fortransmission are widely employed for a variety of purposes ranging froma basic transmission line in public communication channel to ashort-distance network such as a LAN (local area network). Since most ofthe devices connected by these optical fibers are electronic devicesrather than optical devices, optical transceivers are commonly placed atthe interface between the optical fibers and the electronic devices. Anoptical transceiver includes an optical transmitter that receiveselectric signals and converts them into optical signals, and an opticalreceiver that receives optical signals and converts them into electricsignals.

[0003] Optical transceivers are commonly packaged in the form of atransceiver module that can be mounted on a motherboard of one of theelectronic devices. These electronic devices to which an opticaltransceiver may be attached are commonly referred to as “host devices.”As optical transceivers become more prolific, standards are imposed sothat manufacturers of host devices do not have to custom-ordertransceivers. Unfortunately, these standards ultimately becomeconstraints that conflict with the transceiver designs that call forbigger optical transceiver modules. For example, while a size standardimposes a maximum allowable size of a transceiver module, certaincomponents in the optical transceiver module must be placed far apart inorder to reduce crosstalk and electromagnetic interference. Morespecifically, the transmitter and the receiver should be spaced farapart and shielded from each other because the optical transmitter,which requires a relatively high current for modulation of a lightemitting element (e.g., a laser diode), can interfere with the opticalreceiver which operates with a relatively low current obtained from thelight receiving element. Also, to ensure that electrostatic dischargeeffects will not be significant, it is desirable to place the componentsaway from the housing of the optical transceiver module. However, doingso increases the size of the printed circuit board inside the modulesince the edges of the printed circuit boards cannot be utilized, andconflicts with the size restriction imposed by the standard.

[0004] One attempt to meet the size restriction while separating certaincomponents by a minimum distance involves coupling the transmitter andthe receiver to two different sides of a single printed circuit board.FIGS. 1-5 show an exemplary embodiment of a conventional single-boardtransceiver 30 including a transmitter module 32 (e.g., TOSA) and areceiver module 34 (e.g., ROSA) mounted on one printed circuit board(pcb) 36 that is configured to fit inside a standard transceiver modulehousing. If pcb 36 is a double-sided printed circuit board, the receivermodule 34 and the receiver circuitry may be mounted on one surface ofprinted circuit board 36, while the transmitter module 32 and thetransmitter circuitry may be mounted on the other surface of the printedcircuit board. Connector pins 39 are soldered on to pcb 36, as shown inFIG. 2. The connector pins 39 should be arranged to meet theconfiguration imposed by the relevant optical communication standard.Then, as shown by an arrow in FIG. 3, the transceiver 30 with connectorpins 39 is placed in a lower housing 40, which is designed to meet thestandard size restrictions. The lower housing 40 comprises a base 42,sidewalls 44, and a network interface enclosure 46. The networkinterface enclosure 46 is divided into a first section 48 for housingthe transmitter 32 and a second section 49 for housing the receiver 34.The division of the network interface enclosure 46 into two sectionshelps reduce crosstalk between the transmitter 32 and the receiver 34because the lower housing 40 is made of a shielding material. FIG. 4shows a transceiver module 50, which is a combination of the transceiver30 and the lower housing 40. When an upper housing 52 is disposed tocover the lower housing 40, the result is the completely enclosedtransceiver module 50, as depicted in FIG. 5. The upper housing 52 isdesigned to snugly fit around the sidewalls 44 of lower housing 40, andhave slots through which pins 39 can protrude and be coupled to a hostdevice.

[0005] However, the single-board optical transceiver module 50 hasdisadvantages. Where the transmitter 32 and the receiver 34 are coupledto different surfaces of the pcb 36, for example, two controllers (oneon each surface) may be necessary to control both components, raisingthe cost of the transceiver and wasting valuable board surface. Further,since the transmitting circuit is greater in circuit scale than thereceiving circuit, the size of the printed circuit board is, to anextent, determined depending on the circuit scale of the transmittingcircuit. Consequently, a sufficient margin space is left on the surfaceof the printed circuit board where the receiving circuit is to bedisposed, again leading to a waste of valuable board space. As hostdevices operate at higher performance levels with faster data transferrates, it becomes desirable to squeeze more circuitry into an opticaltransceiver module. In light of this increased need to efficiently usedthe volume of the transceiver module, such waste of the board spacebecomes highly undesirable.

[0006] A transceiver configuration that allows a more efficient use ofspace for higher circuit density is desirable.

SUMMARY OF THE INVENTION

[0007] A transceiver module including a primary printed circuit boardand a secondary printed circuit board in an enclosure is presented. Theprimary printed circuit board is coupled to the secondary printedcircuit board by a connector pin that protrudes out of a criticalsurface of the enclosure. The printed circuit boards may be positionedsubstantially parallel to the critical surface of the enclosure. When atransmitter is electrically connected to the primary printed circuitboard and a receiver is electrically connected to the secondary printedcircuit board, the transmitter and the receiver may be positioned in aplane that is also substantially parallel to the plane of the criticalsurface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 depicts a conventional single-board transceiver;

[0009]FIG. 2 depicts the single-board transceiver of FIG. 1 with pins;

[0010]FIG. 3 depicts the transceiver of FIG. 2 and a partial housing;

[0011]FIG. 4 depicts the transceiver of FIG. 2 placed in the partialhousing of FIG. 3;

[0012]FIG. 5 depicts a conventional completely enclosed single-boardtransceiver module;

[0013]FIG. 6A depicts a primary board coupled to a transmitter moduleand a receiver module that is to be used for a first embodiment of theinvention;

[0014]FIG. 6B depicts a secondary board that is to be used for a firstembodiment of the invention;

[0015]FIG. 7 depicts an exemplary pin device that may be used to couplea plurality of boards in accordance with the invention;

[0016]FIG. 8 depicts the primary board of FIG. 6A and the secondaryboard of FIG. 6B combined with the pin device of FIG. 7 to form atransceiver in accordance with the first embodiment of the invention;

[0017]FIG. 9 depicts an optional signal ground plate that may be addedto the transceiver in accordance with the invention;

[0018]FIG. 10 depicts a multi-board transceiver including the signalground plate of FIG. 9 in accordance with the first embodiment of theinvention;

[0019]FIG. 11 depicts a lower housing for a transceiver in accordancewith the invention;

[0020]FIG. 12 depicts a partially enclosed transceiver of the firstembodiment of the invention including the lower housing of FIG. 11;

[0021]FIG. 13 depicts an upper housing for a transceiver in accordancewith the invention;

[0022]FIG. 14 depicts a completely enclosed transceiver module inaccordance with the invention;

[0023]FIG. 15 depicts a primary board coupled to a transmitter modulethat is to be used for a second embodiment of the invention;

[0024]FIG. 16 depicts a secondary board coupled to a receiver modulethat is to be used for the second embodiment of the invention;

[0025]FIG. 17 depicts the primary board and the secondary board coupledwith a pin device in accordance with the second embodiment of theinvention;

[0026]FIG. 18 depicts a tri-ground-plane transceiver including a signalground plane in accordance with the second embodiment of the invention;and

[0027]FIG. 19 depicts a partially-enclosed transceiver module inaccordance with the second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention is directed to an optical transceivermodule, and it will be described in that context. As used herein, a“transceiver” refers to components and circuitry necessary forconverting signals between optical and electrical modes. A “transceivermodule” refers to a transceiver combined with some type of housing orenclosure. Also, as used herein, the words “up,” “top,” and “above” andthe words “down,” “bottom,” and “below” are used in reference to atransceiver or a transceiver module whose base is resting on a surface.

[0029]FIG. 6A depicts a primary board 70, which is a printed circuitboard with a signal ground plane that may have components and circuitryon at least one surface and through-holes 74 along the edges. Theprimary board 70 has conductive zones 76 in select sections of the boardsurfaces including the area around the through-holes 74 and along anedge that is closest to a transmitter module 80 and a receiver module82. Each of the conductive zones 76 along the edges include a long stripof conductive material with through-holes 74 punched through them.Therefore, the through-holes 74 are electrically coupled to each otherby the conductive zones 76, and the circuitry that are connected to eachof the through-holes 74 are automatically connected to each other.

[0030] The conductive zones 76 of the primary board 70 are directlyelectrically connected to the transmitter module 80 and the receivermodule 82 with a conductive means, e.g., flexible connectors 84 and 86.The transmitter module (e.g., TOSA) 80 is a well-known device thatincludes a transmitter (e.g., a laser diode) for receiving electricalsignals and emitting optical signals. The receiver module 82 is awell-known device that includes a component (e.g., a photodiode) forreceiving optical signals and generating corresponding electricalsignals. The connectors 84 and 86 may be any well-known connectiondevices, and may include circuitry. Although other means of connectionmay be used to electrically couple the transmitter module 80 and thereceiver module 82, connectors 84 and 86 are preferably flexibleconnectors because flexible connectors fit into a small space, includenecessary circuitry, allow for short leads 81, 83 from the transmitterand receiver modules 80, 82, and have easily adjustable shapes. Sincethe connectors 84 and 86 need to fit into a small and crowded space,portions of the flexible connectors are cut out to prevent them fromoccupying the space that would be needed for another component of thetransceiver module. The connectors 84 and 86 may have different sizesand shapes, as each of them accommodates different components in itssurrounding. For example, the flexible connector 84 is shaped with acutout 85 to accommodate a structure in the enclosure and the flexibleconnector 86 is shaped with a different cutout 87 that accommodates amounting stud connected to the enclosure (shown below in FIG. 14). Aperson of ordinary skill in the art would understand how to use aflexible connector to electrically couple the transmitter module and thereceiver module to the conductive zones 76.

[0031] The shape of the primary board 70 is approximately a rectangularboard with cutout corners 77, side cutouts 78, and a transmitter cutout79. The cutout corners 77 and the side cutouts 78 accommodate certainparts of the enclosure in which the boards are placed, which is shownbelow. The transmitter cutout 79 is necessary to make space for thetransmitter module 80, which is larger than the receiver module 82. Theprimary board 70 also has an extension 73 on the side of the boardopposite the side that is connected to the transmitter module 80 and thereceiver module 82. The extension 73 is a part of the printed circuitboard with no circuitry or components, and helps prevent the primaryboard 70 from shifting inside the enclosure after the primary board 70is assembled into a transceiver module, as explained below in referenceto FIG. 12. The area of the primary board 70 near the extension 73 mayinclude “keepouts,” or regions where components are not to be placed.

[0032]FIG. 6B depicts a secondary board 60, which is a printed circuitboard that has circuitry on at least one surface and through-holes 64located along two edges. The through-holes 64 of the secondary board 60are positioned to match the positions of the through- holes 74 on thesecondary board 60 so that straight pins can connect the two boards. Thesecondary board 60 includes a signal ground plane and has conductivezones 66 coated with a conductive material. Each of the conductive zones66 are selectively connected to certain parts of the circuitry on thesurface of the secondary board 60. The circuitry may include components,such as a component 62, that emit electromagnetic radiation and heat.The conductive zones 66 surround each of the through-holes 64 withoutall being connected to each other. Thus, the circuitry on the secondaryboard 60 can be selectively coupled to another circuit that is not onthe secondary board 60 through a conductive pin that is inserted intoone of the through-holes 64. The separation of the conductive zones 66around each of the through-holes 64 prevents the circuits that areconnected to each of the through-holes 64 from automatically connectingto one another when conductive pins are inserted into the through-holes64. There are also conductive zones 66 near the edge that would beclosest to the transmitter module 80 and a receiver module 82 when thetransceiver is assembled. Like the primary board 70, the secondary board60 has cutout portions such as corner cutouts 67, a side cutout 68, anda transmitter cutout 69. The purpose of these cutout portions is toaccommodate certain protruding portions of the enclosure in which thesecondary board 60 will be placed. A person of ordinary skill in the artwould know how to achieve the desired shape for the secondary board 60from a standard rectangular-shaped printed circuit board.

[0033]FIG. 7 depicts an exemplary pin device 90 that is used forconnecting the secondary board 60 and the primary board 70. The pindevice 90 includes a set of connector pins 92 and a header 94 that holdsthem together at fixed locations. The connector pins 92 are made of aconductive material and sized to fit snugly through the through-holes 64of the secondary board 60 and the through-through-holes 74 of theprimary board 70. The connector pins 92 are long enough to extendthrough both the secondary board 60 and the primary board 70 and througha critical surface of an enclosure (not shown in this figure) so thatthey can couple to a host device. The header 94 divides the length ofeach connector pin 92 into two sections: an upper pin portion having alength L_(a) and a lower pin portion having a length L_(b). In thepreferred embodiment, the connector pins 90 have a straight section thatis long enough to couple the secondary board 60 and the primary board 70and protrude through a surface of the enclosure. Although this exemplaryembodiment shows a set of five connector pins 92 in the pin device, 90,the invention is not so limited and the pin device 90 may include anynumber of connector pins. The preferred number of pins in a pin device90 depends at least partly on a standard pin layout that is imposed ontransceiver modules. In a 20-pin transceiver module that has 10 pins oneach side, a part of which is shown in FIG. 8, it is preferable to have5 or 10 pins per pin device 90. The header 94, which separates two partswithin a transceiver module, may be made of any nonconductive materialthat is solid enough to provide structural integrity to the transceiver.The header 94 is made of a solid, electrically nonconductive material(e.g., plastic).

[0034]FIG. 8 depicts how the secondary board 60 and the primary board 70are connected with the pin device 90 to form a multi-board transceiver98. Four of the 5-pin pin device 90 are used to completely connect thesecondary board 60 and the primary board 70 in a 20-pin transceivermodule. Preferably, the multi-board transceiver 98 is formed by firstinserting four of the pin devices 90 through the through-holes 74 (FIG.6A) of the primary board 70 until the header 94 contacts the primaryboard 70, then inserting the lower portion of connector pins 92 having alength L_(b) through the through-holes 64 of the secondary board 60 andsoldering the connector pins 92 onto the through-holes 64. Either theheader 94 or the upper portion (L_(a)) of the connector pins 92 aresoldered on to the primary board 70 to provide structural rigidity tothe transceiver 98 and to prevent the two boards from collapsing ontoeach other. The connector 30 pins 92 establish electrical connectionbetween the primary board 70 and the secondary board 60. The extent towhich the connector pins 92 go into the through-holes is set by thelocation of the header 94, which lodges on the top surface of theprimary board 70 after a predetermined length of the connector pins 92extend through the holes.

[0035] Once the primary board 70 and the secondary board 60 areassembled into the transceiver 98 with connector pins 92, the four boardsurfaces are referred to as a primary exterior surface 70 a, a primaryinterior surface 70 b, a secondary interior surface 60 b, and asecondary exterior surface 60 a. One or both of the primary board 70 andsecondary board 60 may be double-sided, providing up to four surfaces onwhich components and circuits can be placed. A person of ordinary skillin the art will understand that components and circuits may be dividedamong the four surfaces in a number of ways to optimize the performanceof the transceiver 98. For example, in one embodiment, the componentsand circuits that operate the transmitter module 80 may be placed on oneboard while the components and circuits that operate the receiver may beplaced on the other board. Separation of the transmitter components andthe receiver components helps reduce crosstalk between the componentsfor each module. In addition, electromagnetic interference may beminimized by placing the noisiest components and the mostnoise-sensitive components as far apart as possible, for example on theprimary exterior surface 70 a and the secondary exterior surface 60 a.This arrangement places two ground planes (one in each board) betweenthe noisiest components and the noise-sensitive components,significantly reducing electromagnetic interference. The ground planesare formed integrally with the printed circuit boards.

[0036]FIG. 9 depicts an optional signal ground plate 100 that may bepositioned near the primary board 70 to provide additionalelectromagnetic interference shielding. The signal ground plate 100 maybe a signal ground plane that is shaped to accommodate various partsaround it. For example, the signal ground plate 100 may have openings102 designed to accommodate large/tall components attached to the topsurface of the primary board 70 (this example does not show suchcomponents). The edges of the signal ground plate 100 that align withthe connector pins 92 have cutouts 104 and holes 106 that accommodatethe connector pins 92. The cutouts 104 are curved portions along theedge that do not contact the connector pins 92 when assembled, while theconnector pins 92 extend through the holes 106 and makes an electricalconnection with the inserted connector pins 92. If the signal groundplate 100 is a signal ground plane, the connector pins 92 that extendthrough the holes 106 are at signal ground, as are all circuits that areconnected to those connector pins 92.

[0037] The signal ground plate 100 includes four signal ground pins 108a, 108 b, 108 c, and 108 d (collectively 108) that are designed toextend through the enclosure like the connector pins 92. The signalground pins 108 are arranged according to the standards imposed onoptical transceivers. In FIG. 9, the signal ground pins 108 are arrangedat four corners of a trapezoid instead of four corners of a rectangle.More specifically, the signal ground pins 108 c and 108 d are arrangedso that they are offset from each other instead of being directly acrossfrom each other. This trapezoidal arrangement is imposed by the MSA.

[0038] The signal ground plate 100 may be made of a rigid material thatdoes not flex easily and effectively blocks electromagneticinterference. Thus, integrating the signal ground pins 108 into thesignal ground plate 100 prevents the signal ground pins 108 frombecoming displaced or bent when a force is applied. The signal groundplate 100 further includes a groove 109 located near the signal groundpins 108 a and 108 b. The groove 109 prevents a 90° angle from formingnear the interface of the signal ground pins 108 a, 108 b and the restof the signal ground plate 100, thereby adding extra stability to thesesignal ground pins. A 90° angle would make the signal ground pins 108 a,108 b prone to breaking.

[0039]FIG. 10 depicts how the signal ground plate 100 is combined withthe multi-board transceiver 98 of FIG. 8 to form a triple-ground-platetransceiver 110. The triple-ground-plate transceiver 110 includes thesecondary board 60, the primary board 70, and the signal ground plate100, each of which includes a signal ground plane. The signal groundplate 100 is placed above the primary board 70 such that parts of thecutouts 104 and the holes 106 lodge on the header 94, and is soldered tothe header 94. The cutouts 104 do not contact the connector pins 92,while the connector pins 92 that extend through the holes 106 areelectrically connected to the signal ground plate 100. Which connectorpins 92 are to be connected to the signal ground plate 100 ispredetermined by an industry standard. The signal ground pins 108 extendupward, in the same direction the connector pins 92 extend. Two of thesignal ground pins 108 are located above the two ends of the extension73 of the primary board 70. Two of the signal ground pins 108 arealigned with one row of connector pins 92, while the other two arealigned with the other row of connector pins 92.

[0040]FIG. 11 depicts a lower housing 120 that forms part of theenclosure for a transceiver module in accordance with the invention. Thelower housing 120 has substantially the same standard dimensions as thelower housing 40 of FIG. 3, and includes a base 122 and a coveredsection 124. The base 122 lies on a plane that is substantially parallelto the critical surface (see FIG. 13) of the enclosure when assembled.The plane on which base 122 lies is also substantially parallel to theplane of the secondary board 60 and the plane of the primary board 70.The covered section 124 is divided into a transmitter section 126 inwhich an optical fiber (not shown) carrying signals output fromtransmitter module 80 terminates, and a receiver section 128 in which anoptical fiber (not shown) carrying signals entering receiver 82terminates. The lower housing 120 may also have corner structures 130near the corners of the base 122 that are farthest away from the coveredsection 124, and the two corner structures 130 are connected with an endwall 132 that extends across the width of the base 122. The end wall 132is designed to block electromagnetic interference by ensuring that thetransceiver 98 is enclosed as completely as possible (i.e., minimize thegap through which electromagnetic interference can escape) when thetransceiver module is assembled. Each of the corner structures 130includes a lower corner shelf 134 and a higher corner shelf 135 thatsupport the primary board 70 and the signal ground plate 100,respectively. Along the longest edge of the lower housing 120approximately halfway down the length of the lower housing 120 is a sideshelf 136 that is about as high as a the lower corner shelf 134. Eachside shelf 136 is connected to a side structure 138. The side shelf 136protrudes from the side structure 138 inward, or toward the inside ofthe enclosure that base 122 forms a part of, effectively forming a shelfon which the primary board 70 can rest. On the outside wall of each sidestructure 138 is a support structure 140. The support structure 140 isto prevent the signal ground pins 108 from bending too far down, asdescribed below in reference to FIG. 12. Protruding from the base 122 isa rib 142 that provides structural strength to the base 122 and ensuresthat the base 122 does not bend easily. As shown above in FIG. 8, theconnector pins 92 extend beyond the bottom surface of the secondaryboard 60. The lower housing 120 being chassis ground, it is undesirablefor the connector pins 92 to come into contact with the base 122.Therefore, the height of the rib 142 is low enough that it will not comein contact with the secondary exterior surface 60 a or the bottomportions of connector pins 92. The rib 142 may be made of the samematerial as the base 122 or a nonconducting material.

[0041] The lower corner shelf 134 and the side shelf 136 support theprimary board 70, thereby helping to keep the primary board 70 and thesecondary board 60 separated. The lower corner shelf 134 and the sideshelf 136 are, therefore, necessarily taller than the rib 142. Among thethree planes in the transceiver 98, namely the primary board 70, thesecondary board 60, and the signal ground plate 100, only the secondaryboard 60 is placed below the level of the end wall 132 since it does nothave an extension 73 like the primary board 70. The transmitter module80 and the receiver module 82, both of which have a cylindrical shape,are supported by the curved support structures 144 located at theinterface of the base 122 and the covered section 124.

[0042]FIG. 12 depicts a partially enclosed transceiver module 150, whichis the triple-ground-plane transceiver 110 (FIG. 10) placed in the lowerhousing 120 (FIG. 11). The secondary board 60, which does not lodge onthe end wall 132, rests on the rib 142 so that the bottom ends of theconnector pins 92 do not contact the chassis ground base 122. The sidecutouts 68 accommodate the side structure 138, and the corner cutouts 67accommodate the corner structures 130 of the lower housing 120. Thesecondary board 60 would not be able to rest on the rib 142 and bepositioned parallel to the base 122 if it were not for the cornercutouts 67, the side cutout 68, and the absence of a counterpart toextension 73.

[0043] The primary board 70 rests on the lower corner shelves 134 andthe side shelves 136, and therefore do not contact the secondary board60. The secondary board 60 and the primary board 70 must be separated bya sufficient distance so that components on the primary interior surface70 b and the components on the secondary interior surface 60 b do notcome into contact. The corner cutouts 77 (see FIG. 6A) accommodate thecorner structures 130 and the side cutouts 78 (see FIG. 6A) accommodatesthe side structure 138. The corner cutouts 77 prevent the primary board70 from sliding around in the plane of the primary board 70. The sidecutouts 78, on the other hand, prevent the primary board 70 from anypivotal or rotational movements. The signal ground plate 100 rests onthe headers 94 and the upper corner shelves 135, and the secondary board60 hangs from the connector pins 92. Thus, by preventing the primaryboard 70 from sliding around or pivoting/rotating, the secondary board60 and the signal ground plate 100 are also fixed in place.

[0044] Although the cutout portions 67 and the edge between the cutoutportions 67 may touch parts of the lower housing 120, the portions thattouch the lower housing 120 are “keepout” sections without circuitry orcomponents. Thus, there is no electric coupling between thechassis-ground lower housing 120 and the secondary board 60.

[0045] The connector 84 has a cutout portion 85 so that the flexibleconnector 84 does not contact the side structure 138. The transmittermodule 80 and the receiver module 82 rest on the curved supportstructures 144 (see FIG. 11). In addition, a port retention bar 146 isplaced on the transceiver module 80 and the receiver module 82 such thatfor each module, the semicircular curve of the support structure 142 andthe semicircular curve of the port retention bar 146 meet to surroundthe module, providing stability and preventing radiation from escapingthrough the transmitter section 126 and the receiver section 128 andinterfering with the operation of the host device. The port retentionbar 146 is pressed down by an upper portion of the enclosure (shownbelow in FIG. 13) when the upper portion is added, and acts as aneffective means of blocking any radiation leak through the transmittersection 126 and the receiver section 128. The curved portion of the portretention bar 146 that is not visible in FIG. 12 are shaped to fitaround the transmitter and receiver modules.

[0046] The secondary board 60 and the primary board 70 are stacked sothat both boards are in a plane parallel to the base 122. Thetransceiver module maintains structural integrity when the boards arestacked in the direction in which the connector pins 92 extend becausethe connector pins 92 extend through through-holes 64, 74 and aresoldered thereon. In the embodiment shown, the transmitter module 80 andthe receiver module 82 are aligned in a plane that is substantiallyparallel to both the critical surface 102 and the stacked boards. Inorder to fit the transmitter module 80 comfortably within the limitedvolume of the enclosure, the shapes of the secondary board 60 andprimary board 70 are altered from the standard rectangular shape throughcutouts 69, 79.

[0047]FIG. 13 depicts an upper housing 160 that is to be combined withthe partially enclosed transceiver module 150 shown in FIG. 12 to form acompletely enclosed transceiver module. The upper housing 160 includes acritical surface 162, sidewalls 164 that are connected to two oppositeedges of the critical surface 162, and an end wall 166 connected to athird edge of the critical surface 162. The critical surface 162 has aconnector pin cutout 168 through which the connector pins 92 extend whenthe upper housing 160 is assembled with the partially enclosedtransceiver module 150. Although the connector pin cutout 168 may havedifferent shapes, e.g., two long slits instead of a plurality of holesthat each accommodates one connector pin 92, the plurality of holes arepreferred because they allow less electromagnetic radiation to escape.

[0048] The upper housing 160 also has signal ground pin cutouts 170 a,170 b, 170 c, and 170 d (collectively 170) that accommodate the signalground pins 108. The signal ground pin cutouts 170 a and 170 b areshaped to be just large enough for the signal ground pins 108 a and 108b to extend through them without touching the edges of the cutouts 170 aand 170 b. The signal ground pin cutouts 170 c and 170 d are largeenough to accommodate both the support structures 140 and the signalground pins 108 c, 108 d. The upper housing 160 is securely coupled withthe lower housing 120 when the signal ground pin cutouts 170 c, 170 dand small side cutouts 169 snap over the support structures 140 andother protrusions on the lower housing 120, respectively. The upperhousing 160 touching the side structure 138 or the support structure 140is not problematic since both the upper housing 160 and the lowerhousing 120 are chassis ground. A pair of mounting stud openings 172 arelocated to receive mounting studs. The mounting studs, which arerequired by the MSA standard, are preferably coupled to the upperhousing 160 before the upper housing 160 is combined with the lowerhousing 120.

[0049]FIG. 14 depicts a transceiver module 180, which is the upperhousing 160 combined with the partially enclosed transceiver module 150.The connector pins 92 extend through the connector pin holes 168. Thesignal ground pins 108 a and 108 b extend through the signal ground pinopenings 170 a and 170 b. The signal ground pins 108 c and 108 d extendthrough the signal ground pin openings 170 c and 170 d along with thesupport structure 140.

[0050] The mounting studs 182 are fixed in place to protrude from themounting stud openings 172 (see FIG. 13). The mounting studs 182 may bechassis-ground or isolated. If the mounting studs 182 are isolated,mounting stud insulators 184 are necessary to prevent the mounting studs182 from contacting the chassis-ground upper housing 160. The mountingstud insulators 184 may first be injection molded into the mounting studopenings 172, and then the mounting studs 182 may be pressed into theinsulators 184. If insulators 184 are not necessary, the mounting studs182 may be directly molded into the mounting stud openings 172. Themounting studs 182 being isolated is advantageous in that it allows forcustomization later according to the needs of the host device. Themounting studs 182 can be chassis-ground if so required by the hostdevice.

[0051] FIGS. 15-20 depict a second embodiment of the transceiver that isshown in FIG. 6A-FIG. 14. The main difference between the transceiver ofthe first embodiment (FIGS. 6A-14) and the transceiver of the secondembodiment (FIGS. 15-20) is the arrangement of the transmitter moduleand the receiver module.

[0052]FIG. 15 depicts a primary board 202 coupled to a transmittermodule 204. The primary board 202 is a printed circuit board including aground plane that has circuitry and components on at least one surface.The transmitter module 204 is connected to the primary board 202, aportion of which is cut out to make room for the transmitter module 204.The transmitter module (e.g., TOSA) 204 is a well-known device similarto the transmitter module 80. The primary board 202 has through-holes205 along two edges, and the two edges are coated with a conductivematerial to create conductive zones 206. The basic shape of the primaryboard 202 is similar to that of the primary board 70 (FIG. 6A) withsimilar cutouts. However, unlike the primary board 70, which isconnected to both a transmitter module and a receiver module, theprimary board 202 is coupled only to the transmitter module 204.

[0053]FIG. 16 depicts a secondary board 210. The secondary board 210 isa printed circuit board including a signal ground plane and circuitry onat least one surface, and is generally similar to the secondary board 60of FIG. 6B except that the secondary board 210 is directly connected toa receiver module 214. The secondary board 210 has a conductive zone 212that is physically connected to the receiver module (e.g., ROSA) 214,which is a well-known device similar to the receiver module 82 (FIG.6A). The receiver module 214 may be connected to the conductive zone 212by any of the conventional methods, and preferably a flexible ribbonconnector 216. The secondary board 210 has through-holes 218 along theedges that include electrically conductive sections connected to thecircuitry on the secondary board 210.

[0054]FIG. 17 depicts a transceiver 220 that includes the primary board202 and the secondary board 210 connected with pin devices 90 (see FIG.7). The primary board 202 and the secondary board 210 are connected insubstantially the same manner as the primary board 70 and the secondaryboard 60 (see FIG. 8). The lower pin portion (length L_(b)) of theconnector pins 92 are inserted through the through-holes 205 of theprimary board 202 until the header 94 comes in contact with the primaryboard 70. The header 94 may be affixed, e.g., with an adhesive, to theprimary board 202 by any conventional manner that does not affect theelectrical connection between the circuitry on the board and theconnector pins 92. Then, the lower portion of the connector pins 92 areinserted through the through-holes 218 of the secondary board 210 andthe connector pins 92 are soldered to the through-holes 205, 218. Whenthe connector pins 92 extend through the through-holes 205, 218, theycome in contact with the conductive zones 206, 219 near thethrough-holes. Thus, the connector pins 92 establish an electrical aswell as physical connection between the primary board 202 and thesecondary board 214.

[0055] Once the primary board 202 and the secondary board 204 areassembled in this manner, there are up to four surfaces on whichcircuitry and components can be placed. These four surfaces are aprimary exterior surface 202 a, a primary interior surface 202 b, asecondary exterior surface 210 a, and a secondary interior surface 210b. Since the primary board 202 and the secondary board 210 are connectedto one module each, most circuitry relating to the operation of thetransmitter module 204 may be placed on the primary board 202, whilemost circuitry relating to the operation of the receiver module 214 maybe placed on the secondary board 210 to minimize undesirable crosstalkbetween the transmitter components and the receiver components. Thenoisiest transmitter components may be placed on the primary exteriorsurface 202 a, while the most noise-sensitive receiver components may beplaced on the secondary exterior surface 210 a. Also, board space may beconserved and transceiver manufacturing cost may be reduced by usingonly one controller chip for both boards instead of one controller chipfor each board. The multi-board configuration of transceiver 220provides circuit designers with more options by providing more boardspace that is away from the board periphery. The gap between the primaryinterior surface 202 b and the secondary interior surface 210 b not onlyallow components to comfortably fit on the surfaces, but also allows airflow between the boards. The air flow helps heat dissipation forcomponents attached to board surfaces.

[0056]FIG. 18 depicts a tri-ground-plane transceiver 230 that includesthe multi-board transceiver 220 combined with the signal ground plane100 (FIG. 9). The signal ground plane 100 is added to the multi-boardtransceiver 220 in a substantially similar manner that it is added tothe multi-board transceiver 98 (FIG. 8) to form tri-ground-planetransceiver 110 (FIG. 10).

[0057]FIG. 19 depicts a method of assembling the tri-ground-planetransceiver 230 with the lower housing 120 (see FIG. 11) to form apartially-enclosed transceiver module 240. As the outline of atransceiver module is dictated by an industry standard, thetri-ground-plane transceiver 110 and the tri-ground-plane transceiver 98are able to fit into the same housing. The lower housing 120 is chassisground and made of an RF-shielding material so that the radio frequencyemissions from the components on primary board 202 and the secondaryboard 210 do not interfere with the operation of components outside thetransceiver module, and vice versa. The tri-ground-plane transceiver 230is placed inside the lower housing 120 in substantially the same way thetri-ground-plane transceiver 98 is placed inside the lower housing 120,with the planes of the primary board, the secondary board, and thesignal ground plane being parallel to the base 122 and the connectorpins 92 extending in a direction orthogonal to these planes. Since thereceiver module 214 is coupled to the secondary board 210, which ispositioned closer to the base 122, extra caution must be taken to ensurethat the connector 216 does not come in contact with the base 122 andespecially the rib 142 (see FIG. 11). The connector 216 may be shapeddifferently from the connector 86 that was used to connect the receivermodule to the primary board in FIG. 6A, to avoid coming in contact withthe rib 142.

[0058] The upper housing 160 of FIG. 13 is added to thepartially-enclosed transceiver module 230 to form a transceiver modulethat looks substantially similar to the transceiver module of FIG. 14.The outlines of the transceiver modules, which is dictated by theindustry standard, is the same between the embodiments. Since theconnector pins 92 are used to couple the optical transceiver with a hostdevice, the critical surface 162 is the surface of upper housing 210that is closest to the host device when the optical transceiver moduleis assembled. The upper housing 160 is designed so that when it isassembled with the lower housing 120, the primary board 202 and thesecondary board 210 are completely enclosed except for the connectorpins 92 that protrude through the pin openings 168. Preferably, at leastsome of the connector pins 92 have a straight portion that extends in adirection perpendicular to the planes of the boards 202 and 210 towardto a host device. As a consequence, the base 122 and the criticalsurface 162 are both perpendicular to the straight portion of theconnector pins 92 that couple the transceiver module to the host device.Preferably, the base and the housing surface that is to be attached tothe host device are the largest surfaces of a rectangular-shaped module.This way, the surface area of the primary board 202 and the secondaryboard 210 that is away from the enclosure is maximize.

[0059] A person of ordinary skill in the art would understand that thepreferred positioning and alignment of the transmitter module and thereceiver module are a function of the shapes and sizes of each of thesemodules and of the size and shape limitations imposed on the transceivermodule, and the invention is not limited to the embodiments shown. Forexample, the transmitter module 62 and the receiver module 64 may beplaced in a plane that is perpendicular to the critical surface 102 andthe stacked boards.

[0060] The multi-board transceiver module of the invention provides thebenefit of lowering manufacturing costs by reducing scrap parts. Sincecomponents and circuitry are spread out over multiple boards instead ofbeing squeezed into one board, and since the components on each boardare tested separately, only one board needs to be scrapped if there is adefective component. The remaining components on the other board canstill be used. For example, in the second embodiment where the receivermodule and transmitter module are connected to different boards and thereceiver module does not pass the quality test, only the board connectedto the receiver module needs to be scrapped. This is different from thesituation involving single-board configurations where if one part failsthe test, all the transceiver components would have to be scrapped.

[0061] A person of ordinary skill in the art would understand thatvarious modifications may be made to the multi-board transceiver modulesdescribed herein without straying from the scope of the invention. Forexample, while the transmitter module and the receiver module are shownto be connected to one or more of the boards by flexible ribbonconnectors, any well-known method for electrically coupling two partsmay be used instead of flexible connectors. Wires may be used.Alternatively, the transmitter module and the receiver module may bedirectly mounted on their respective boards. Also, the through-holes onthe boards are not limited to being holes. The through-holes may be anyopen or closed aperture or notch.

[0062] While the foregoing has been with reference to a particularembodiment of the invention, it will be appreciated by those skilled inthe art that changes in this embodiment may be made without departingfrom the principles and spirit of the invention, the scope of which isdefined by the appended Claims.

What is claimed is:
 1. An optical transceiver module comprising: anenclosure having a critical surface; a primary printed circuit board anda secondary printed circuit board disposed in the enclosure; atransmitter module electrically connected to one of the primary andsecondary printed circuit boards; a receiver module electricallyconnected to one of the primary and secondary printed circuit boards;and at least one connector pin connected to the primary and secondaryprinted circuit boards and extending through the critical surface. 2.The transceiver module of claim 1 wherein the at least one connector pinis straight.
 3. The transceiver module of claim 1 further comprising afirst circuit on the primary printed circuit board and a second circuiton the secondary printed circuit board, wherein the connector pin ismade of a conductive material and electrically connects the firstcircuit to the second circuit.
 4. The transceiver module of claim 1wherein the primary and secondary printed circuit boards are disposedsubstantially parallel to each other and to the critical surface.
 5. Thetransceiver module of claim 4, wherein the primary printed circuit boardis disposed between the critical surface and the secondary printedcircuit board.
 6. The transceiver module of claim 1 wherein the criticalsurface is a largest surface of the enclosure.
 7. The transceiver moduleof claim 1 wherein the enclosure comprises a lower portion and an upperportion that fit together to enclose the printed circuit boards, theupper portion having a sidewall including a hole and a notch, whereinthe hole is designed to fit over a protrusion of the lower portion andthe notch fits into a receded section of the lower portion having ashape that complements the notch, the hole and the notch securelylocking the lower portion and the upper portion together by being placedover the protrusion and in the receded section, respectively.
 8. Thetransceiver module of claim 1 further comprising a controller chipelectrically connected to one of the primary and secondary printedcircuit boards, wherein the controller chip controls the transmittermodule and the receiver module.
 9. The transceiver module of claim 1further comprising: electrical components and circuitry for operation ofthe transmitter module that are connected to the primary printed circuitboard; and electrical components and circuitry for operation of thereceiver module that are connected to the secondary printed circuitboard.
 10. The transceiver module of claim 1 wherein the connector pinextends in a direction that is substantially orthogonal to a plane ofthe critical surface, a plane of the primary printed circuit board, anda plane of the secondary printed circuit board.
 11. The transceivermodule of claim 1 wherein the primary printed circuit board comprises aplurality of first through-holes and the secondary printed circuit boardcomprises a plurality of second through-holes wherein the first andsecond through-holes are coated with a conductive material to create aconductive zone, the conductive zone around each of the firstthrough-holes being connected to one another and the conductive zonearound each of the second through-holes being separate.
 12. Thetransceiver module of claim 11 wherein the conductive zones areconnected to a first circuitry located on the primary printed circuitboard and a second circuitry located on the secondary printed circuitboard so that the connector pin electrically connects the firstcircuitry and the second circuitry by extending through the first andsecond through-holes.
 13. The transceiver module of claim 1 furthercomprising: a first flexible connector connecting the transmitter moduleto one of the primary and secondary printed circuit boards; and a secondflexible connector connecting the receiver module to one of the primaryand secondary printed circuit boards, wherein the first flexibleconnector and the second flexible connector are shaped and positioned toavoid contacting nearby components.
 14. The transceiver module of claim1 further comprising a signal ground plane including signal ground pins,the signal ground plane being disposed in the enclosure between thecritical surface and one of the primary and secondary printed circuitboards so that the signal ground plane is substantially parallel to aplane of the critical surface, and the signal ground pins extendingthrough the critical surface.
 15. The transceiver module of claim 14wherein a region of the signal ground plane that is near the signalground pins is shaped to avoid forming a ninety-degree angle on thesignal ground plane, thereby reducing a likelihood of breakage.
 16. Thetransceiver module of claim 14 wherein the signal ground plane contactsa preselected one of the at least one connector pin to make thepreselected connector pin signal ground.
 17. The transceiver module ofclaim 14 wherein the connector pin comprises an upper portion pin, aheader, and a lower portion pin and the header is located between two ofthe signal ground plane, the primary printed circuit board, and thesecondary printed circuit board to keep the two separated.
 18. Thetransceiver module of claim 14 wherein the enclosure comprises a lowerportion and an upper portion that fit together to enclose the printedcircuit boards, wherein the upper portion comprises signal ground pinopenings through which the signal ground pins extend, at least one ofthe signal ground pin openings being shaped to fit over a protrudingstructure on the lower portion to lock the upper portion and the lowerportion together.
 19. The transceiver module of claim 1 furthercomprising a port retention bar that covers a portion of the transmittermodule and the receiver module, the port retention bar being pressedbetween a base of the enclosure and a critical surface of the enclosureto form an inner wall that blocks radiation from escaping thetransceiver module.
 20. The transceiver module of claim 1 wherein theenclosure is chassis-ground.
 21. The transceiver module of claim 1wherein the enclosure further comprises a mounting stud protruding froma surface of the enclosure, the mounting stud being electricallyisolated from the primary printed circuit board and the secondaryprinted circuit board.
 22. The transceiver module of claim 21 whereinthe mounting stud is chassis-ground.
 23. The transceiver module of claim21 further comprising a mounting stud insulator located between themounting stud and the surface of the enclosure, the mounting stud beingelectrically isolated.
 24. The transceiver module of claim 1 wherein theprimary printed circuit board and the secondary printed circuit boardeach has at least one notch located along at least one edge and designedto fit with a structure protruding from an inside wall of the enclosureso as to keep the printed circuit boards fixed at predeterminedpositions inside the enclosure.
 25. The transceiver module of claim 1further comprising a first ground plane physically coupled to theprimary printed circuit board and a second ground plane physicallycoupled to the secondary printed circuit board.
 26. An transceivermodule comprising a transmitter that is electrically connected to aprimary printed circuit board and a receiver that is electricallyconnected to a secondary printed circuit board, wherein the transmitterand the receiver are positioned adjacent to each other along a line in afirst direction and the primary printed circuit board and the secondaryprinted circuit board are positioned adjacent to each other along a linein a second direction substantially perpendicular to the firstdirection.
 27. An optical transceiver module comprising: an enclosurehaving a critical surface; a primary and secondary printed circuitboards disposed in the enclosure, wherein the primary and secondaryprinted circuit boards are parallel to each other and to the criticalsurface; a transmitter module connected to one of the primary andsecondary printed circuit boards; a receiver module connected to one ofthe primary and secondary printed circuit boards; and at least oneconnector pin connected to at least one of the primary and secondaryprinted circuit boards and extending through the critical surface. 28.The optical transceiver module of claim 27, wherein the transmittermodule and the receiver module are disposed in a plane parallel to thecritical surface.
 29. The optical transceiver module of claim 28,wherein the primary printed circuit board is disposed between thecritical surface and the secondary printed circuit board.
 30. Theoptical transceiver module of claim 28, wherein each of the primary andsecondary printed circuit boards includes a through-hole, and whereinthe connector pin is electrically connected to the through-hole on eachprinted circuit board.
 31. An optical transceiver module comprising: anenclosure; a transmitter module and a receiver module disposed insidethe enclosure; and three ground planes disposed inside the enclosure.32. An optical transceiver module comprising a signal ground region, achassis ground region, and an electrically isolated conductive region.33. A method of configuring an optical transceiver module, the methodcomprising: placing a primary printed circuit board and a secondaryprinted circuit board in an enclosure having a critical surface;electrically connecting a transmitter module to one of the primary andsecondary printed circuit boards; electrically connecting a receivermodule to one of the primary and secondary printed circuit boards; andconnecting the primary printed circuit board and the secondary printedcircuit board with at least one conductive connector pin that protrudesthrough the critical surface.
 34. The method of claim 33, furthercomprising positioning the connector pin so that it extends in adirection substantially perpendicular to the critical surface and to theprimary and secondary printed circuit boards.
 35. The method of claim33, wherein the connecting comprises placing the connector pin incontact with an electrically conductive section of the primary printedcircuit board and an electrically conductive section of the secondaryprinted circuit board so that a first circuitry on the primary printedcircuit board is electrically coupled to a second circuitry on thesecondary printed circuit board.
 36. The method of claim 35, wherein theelectrically conductive sections include through-holes located on theprimary and the secondary printed circuit boards.
 37. The method ofclaim 33 further comprising positioning the primary printed circuitboard and the secondary printed circuit board in planes substantiallyparallel to the critical surface.
 38. The method of claim 33 furthercomprising positioning the transmitter module and the receiver module ina plane substantially parallel to the critical surface.
 39. The methodof claim 33 wherein the critical surface is the largest surface of theenclosure.
 40. The method of claim 33 further comprising electricallyconnecting a controller chip to one of the primary and the secondaryprinted circuit boards, wherein the controller controls the operation ofthe transmitter module and the receiver module.
 41. The method of claim33 further comprising positioning a transmitter circuitry for operatingthe transmitter module on the primary printed circuit board andpositioning a receiver circuitry for operating the receiver module onthe secondary printed circuit board.
 42. The method of claim 33 furthercomprising positioning noisy components on an exterior surface of theprimary printed circuit board and noise-sensitive components on anexterior surface of the secondary printed circuit board, an exteriorsurface being a surface that is farthest from the other printed circuitboard.
 43. The method of claim 33, wherein at least one of thetransmitter module and the receiver module is connected to one of theprimary and the second printed circuit boards with a flexible connectorshaped to avoid touching nearby components.
 44. The method of claim 33wherein the enclosure is chassis-ground.
 45. The method of claim 33further comprising providing a first ground plane for a first circuit onthe primary printed circuit board and a second ground plane for a secondcircuit on the secondary printed circuit board.
 46. The method of claim33 further comprising combining an upper housing and a lower housing toform the enclosure that surrounds the primary and secondary printedcircuit boards, the combining comprising: locking the upper housing tothe lower housing by inserting a protrusion on the lower housing into ahole on the upper housing; and preventing the upper housing from slidingon the lower housing by placing a notch on the upper housing in areceded section on the lower housing having a shape that complements thenotch.
 47. The method of claim 46, further comprising placing a mountingstud on the upper portion of the enclosure before the combining.
 48. Themethod of claim 46, further comprising: injection molding a mountingstud insulator into a mounting stud hole on a surface of the upperhousing; and pressing a conductive mounting stud into the injectionmolded insulator.
 49. The method of claim 33, wherein the primary andthe secondary printed circuit boards each include a ground plane,further comprising disposing a third ground plane between the primaryprinted circuit board and the critical surface to further reduceradiation leakage.
 50. The method of claim 33, wherein the connector pinincludes a lower pin portion, a header made of a nonconductive material,and an upper pin portion, wherein the connecting comprising: inserting alower pin portion through first conductive holes on the primary printedcircuit board until the header contacts the primary printed circuitboard; inserting the lower pin portion through second conductive holdson the secondary printed circuit board; and soldering the lower pinportion to the first and second conductive holes to prevent the primaryprinted circuit board and the secondary printed circuit board fromcontacting each other.
 51. The method of claim 50, further comprisingplacing a signal ground plane on the header so that the signal groundplane and the primary printed circuit board are separated by the header.52. The method of claim 51, further comprising signal grounding aselected connector pin by putting the selected connector pin in contactwith the signal ground plane.
 53. The method of claim 33, furthercomprising forming at least one cutout along an edge of at least one ofthe primary printed circuit board and the secondary printed circuitboard and placing the printed circuit boards in the enclosure so thatthe at least one cutout fits around a protruding structure on an innerwall of the enclosure to prevent the primary printed circuit board andthe secondary printed circuit board from moving inside the enclosurelaterally, rotationally and pivotally.
 54. The method of claim 33,further comprising: placing a port retention bar on the transmittermodule and the receiver module, the port retention bar having a curvedsection to accommodate the transmitter module and the receiver module;and pressing the port retention bar between two opposing surfaces of theenclosure so as to form a tight seal and reduce radiation leakage.
 55. Amethod of configuring an optical transceiver module, the methodcomprising: placing a primary printed circuit board and a secondaryprinted circuit board in an enclosure having a critical surface so thatthe primary printed circuit board and the secondary printed circuitboard are substantially parallel to the critical surface; electricallyconnecting a transmitter module to one of the primary and secondaryprinted circuit boards; electrically connecting a receiver module to oneof the primary and secondary printed circuit boards; and connecting aconnector pin to at least one of the primary printed circuit board andthe secondary printed circuit board wherein the connector pin protrudesthrough the critical surface.
 56. The method of claim 55 furthercomprising positioning the transmitter module and the receiver module ina plane parallel to the critical surface.
 57. The method of claim 55further comprising positioning the primary printed circuit board betweenthe secondary printed circuit board and the critical surface.
 58. Amethod of reducing radiation leakage from a transceiver module, themethod comprising: placing a port retention bar over the transmittermodule and the receiver module so that a curved section of the portretention bar joins a curved section of an enclosure base to form aframe that surrounds the transmitter module and the receiver module, theframe having an inner outline that matches a cross section of thetransmitter module and the receiver module and an outer outline thatmatches a cross section of an enclosure that houses the transmittermodule and the receiver module; and combining an upper housing and alower housing to form the enclosure such that the enclosure base and acritical surface opposite the enclosure base press the curved section ofthe port retention bar against the curved section of the enclosure baseto form an inner wall between a section of the enclosure housing acircuitry for the transmitter module and the receiver module and anopening through which signal carrying medium extends out of theenclosure.